Andrew Chennells, South Scarle, Lincolnshire

ONION STORAGE COSTS NOTHING TO CRY ABOUT

Lincolnshire growers G H Chennells Farms Ltd are benefiting from a new onion store that gives them complete control over the store’s temperature and atmosphere, making it easier to meet their key aims: providing quality onions to the processing sector, while reducing energy costs and their carbon footprint.

The 2,400 tonne capacity store was designed and built by Crop Systems Ltd, of Happisburgh, Norfolk, which had previously installed potato stores for the company, which is based at Clay Farm, South Scarle, near Lincoln.

Both the onion and potato stores enable Chennells to achieve better quality crops, while consuming lower levels of inputs and power during the storage period.

The bulk onion store includes several innovative features, including tapering floor ducts that ensure an even supply of air throughout the store. Each duct can be isolated or partially opened using a guillotine door, so onions can be dried efficiently even when the store is only partly loaded, or if different batches of onions are loaded in at different moisture levels.

The refrigeration unit contains a bank of six compressors, one of which is variable speed. They can be switched on and off automatically, minimising electricity use and ensuring cooling capacity always matches requirements:

“We can vary airflows using inverter drives on all fans, adjust the burner position in relation to the fans to maintain the correct airspeed through the burner and vary the output of the fridge unit. It gives us total flexibility and ensures we achieve good results with minimum wastage”, says Andrew.

The central vent tapers from eight feet wide at the wall where the fans are located to four foot wide at the far side of the store, while all cross vents taper towards the end:

“We need to start drying the onions the moment they come into the store to avoid bacterial rots, and skin staining and then dry out the freshly topped necks. We might start with just 200 or 300 tonnes in store, and that ability to infinitely vary airflow by reducing fan speed and isolate areas of the floor is important in terms of crop quality, energy cost and carbon footprint”.

“We aim to leave them in windrows for up to 48 hours, before loading them into the store. But if the weather forecast turns wet we need them in store immediately, even though it means they come in at much higher moisture levels and we need to dry them for longer, at a much higher cost”.

The control system makes it easy to maintain the desired humidity by mixing air from outside the store as needed. After drying, they use ambient air if available or refrigeration to pull the temperature down. The controller is programmed to cool the crop to one degree C when using refrigeration, or zero when suitable ambient air is available. This avoids using refrigeration during the day when it is below freezing at night, during the winter:

“Using inverters and variable speed fans also saves energy, as we can run a fan at 80% speed for half the electricity it would consume at 100% speed. That makes a huge difference to running costs”, says Andrew.

He chose Crop Systems Ltd for the job because they have already installed similar systems in some of the potato stores they use, and have helped them achieve suppressant usage levels of less than half conventional stores: “We knew they had the ability to think outside the box and come up with something innovative. Every aspect of this store is controllable”.

Chennells grow potatoes for crisping that need to be stored at between eight and 12 degrees C, and so need to be treated with a sprouting suppressant:

“The fan system in our bulk stores helps us use about half what we do in conventional box stores, which is both a cost and an environmental advantage”.

By running their fans very slow – down to 15% of full speed – they ensure suppressant spreads evenly and does not deposit on the fans themselves: “The system ensures distribution is even right through the store and avoids over-application, which would be difficult without that extent of control”.